An infant <90 days of age with fever (usually defined as >38C) is very commonly encountered in physician practices in the community and hospital-based emergency departments. Approximately 200,000 such infants are seen in the United States each year; 5-14% of whom will have a serious and potentially life-threatening infection. Because these babies often do not have overt signs of infection, the adjunctive laboratory testing is often quite extensive including a lumber puncture for evaluation and culture, blood culture, and urinalysis and culture studies (known as the rule out sepsis workup) often followed by empiric antimicrobial therapy and hospitalization for close monitoring. Available guidelines that have defined this approach are >20 years old and based on 20-30 year old data. Given various interventions that have lowered the incidence of serious bacterial infection in neonates, and the availability of rapid tests to diagnose less serious, but exceedingly common viral infections in this age group, it is quite possible that clinicians are being too conservative in their management of these babies in 2014. The American Academy of Pediatrics recognizes this reality and is developing a first-ever guideline to assist clinicians. In their process, several knowledge gaps have been identified that, if data were available, would greatly assist this task. Our Aim in this project is to generate unique data, from nationally representative datasets, in three areas of importance in this regard: 1) the number of and the epidemiologic characteristics of hospitalizations for infants with fever; 2) the extent of harm and adverse events these babies may sustain from procedures and treatments received while in the hospital; and 3) the economic impact of the